A question for the engineers amongst you.

I'm working on a rather tired Webley Viscount which is showing wear at some of the usual places. One area is the end block retaining holes, which are a bit slack and worn. The retaining grub screw through the block is missing, and the pin shows signs of having been driven out with the screw still fitted. The pin ends are mushroomed.

So to the point - I'm considering drilling the holes and end block oversize and making a new pin to tighten everything up. Standard pin diameter is 8.28mm, and I doubt if 8.5mm will be enough, so probably 11/32" (8.731mm) or 9mm. Question is, what material would you recommend to make the retaining pin from? Clearly it has to be machinable, unless I go with 9mm and hope that stock 9mm rod is a good fit?

All thoughts appreciated.